1. Background of the Invention
The invention in general relates to controlling the operation of electromagnets and more particularly to the control of electromagnets useful for driving fuel intake or exhaust valves of internal combustion engines between their open and closed positions.
2. Description of the Prior Art
It is well known to utilize electromagnets for driving fuel intake and exhaust valves, hereinafter referred to as gas exchange valves, of internal combustion engines. As will be appreciated proper control of such electromagnets is tantamount to flawless functioning of the valves and engines.
A valve of the kind under consideration is normally held in a neutral position, i.e. a position intermediate its open and closed positions, by the bias of a pair of counteracting springs, and it may be driven into its open or closed position by electromagnets the armatures of which may be operatively connected to the valve. Driving such a valve into its open or closed position, hereinafter referred to as the terminal position, requires energization of the coil of the respective electromagnet with current of a level sufficiently high to pull or push, as the case may be, the armature into engagement with the stator. Once such engagement has taken place the current may be reduced to a level sufficient to maintain the engagement. Hereinafter it will be assumed that upon solenoid energization the armature is pulled into engagement with its stator.
Conventional methods of providing reduced level cycling current may utilize freewheeling circuits connected in parallel with the electromagnet. An arrangement of this kind is disclosed, for instance, by West German patent specification DE-OS 2425585.
Such devices suffer from an inherent problem: Their reduced level holding current phase must not be initiated until after the high level current energization phase has been successfully concluded by the attraction of the armature of the electromagnet into engagement with the stator; for while such reduced level holding current is sufficient for maintaining the armature in its engagement with the stator it is incapable of driving the armature there. Hence, premature initiation of the reduced current phase would prevent the armature from being pulled into engagement with the stator. This, in turn, would result in faulty valve and engine operation.
Circuits have become known which measure or monitor the increase in current during the energization or driving phase of electromagnetic coils and for detecting a temporary drop or break in the rising current slope as an indication of the engagement of the armature with the stator. However, such circuits have been found not to function with the degree of reliability absolutely necessary for flawless engine operation, for their functioning is strongly dependent upon the supply voltage, and they have been found to be particularly prone to malfunction at increases in the supply voltage.
West German patent specification DE-OS 33 26 605 teaches a circuit for monitoring the stroke position of an armature during an operational cycle of an electromagnet. This is accomplished by energizing the electromagnet with direct current with an alternating current superimposed there.
Since the inductance of the electromagnet differs depending upon whether or not the armature is in engagement with the stator, the value of the a.c. component differs correspondingly. Thus, by monitoring the value of the a.c. component the system aims at detecting engagement of the armature with the stator.
However, such a circuit is relatively complicated and requires precise and sophisticated current measuring methods.
It is, therefore, an object of the invention to provide a simple and effective method of and apparatus for detecting the position of an armature in a solenoid during its operation.
It is also an object of the invention to provide for a novel method and apparatus for detecting whether an armature has been attracted into engagement with its stator during an operational cycle of an electromagnet.
A particular object of the invention resides in comparing the frequency of current pulses cycling between upper and lower limits in a freewheeling circuit of an electromagnet during engagement of the armature with the stator against a reference frequency and to connect the electromagnet to a current source whenever a difference exceeding a predetermined value is detected.
A further object of the invention is to improve the performance of internal combustion engines with electromagnetically driven fuel intake and exhaust valves by monitoring their holding current pulses.
Other objects will in part be obvious and will in part appear hereinafter. The invention accordingly comprises a mechanism and system possessing the construction, combination of elements and arrangements of parts which are exemplified in the detailed disclosure.